Method for making an aerosol housing with threaded neck

ABSTRACT

Process for manufacturing a metal can ( 1 ) equipped with a threaded neck on which any type of removable head can be fitted, comprising at least the following steps:  
     a) production of a can with a bottom and a cylindrical or shaped wall  
     b) formation of a neck ( 4 ) at the open end of the can  
     c) use of a ring ( 5 ) equipped with a spindle hole ( 52 ) and a thread ( 54 ) over its outer surface ( 55 ), and sleeve fitting of the spindle hole ( 52 ) in the said ring ( 5 ) around the neck ( 4 ) formed in the previous step,  
     and characterized in that it also includes the following step:  
     d) plastic expansion of the said neck ( 4 ), the diameter of the outer surface ( 42 ) of the neck ( 4 ) being expanded to exceed the value of the inner diameter of the spindle hole ( 52 ) of the ring ( 5 ) when at rest.

TECHNICAL DOMAIN

[0001] This invention relates to a process for making cans made of a lowcarbon steel or aluminum alloy, manufactured by deep drawing, drawingand ironing or extrusion, in which the inner wall is covered with aprotective coating and which are equipped with a threaded neck designedto fix any type of removable head, for example aerosol spraydistribution heads, of the eco-refill type, but also for the attachmentof a closing cap.

STATE OF ART

[0002] According to standard practice as described in GB 1 445 758, canswith a bottom and a cylindrical wall are manufactured starting fromround and flat pieces made of low carbon steel or aluminum alloy, andusing deep drawing, drawing and ironing of blanks or backward extrusion(impact extrusion) of slugs. Once formed, these cans are usuallyvarnished on their inner surface, and painted and/or varnished on theirouter surface. The open end of the can is then formed to have acylindrical neck with a smaller diameter, and a strong plasticdeformation is then applied by necking.

[0003] For practical reasons to facilitate application with a roller ora spray gun, it is better to apply the paint or varnish on thecylindrical surface before necking. The varnish on the inner surface isnecessary for many types of applications, in order to prevent contactbetween the bare metal and the contents of the can. The metallic surfacemust be well protected throughout the period during which the can isbeing used and it is important that the inner varnish covers thissurface fully and continuously. Prior art includes paints and varnishthat remain undamaged during necking.

[0004] Since the metal used (low carbon steel or aluminum alloy) is aninexpensive and easy-to-recycle packaging material, it seemed a goodidea to develop receptacles onto which aerosol spray distribution headsor covers could be screwed, as is the case for glass and plasticbottles. For example, the receptacle could then be sold full and ascrewed cap could be fitted onto it. The user screws and unscrews thedistribution head, designed for multiple use, according to his needs.The receptacle could then be refilled, or the consumer could throw itaway with the rest of his waste, and it could be taken for recycling.

[0005] In order to obtain this type of metallic receptacle satisfyingthe “eco-refill” principle, it must be possible to make a thread, forexample on the neck of the receptacle, in order to participate in theattachment of any type of head. This thread must not damage the varnishlayer described above, that has been subjected to necking in order toform the neck, and which must maintain its protective properties in allcases.

[0006] In the past, the thread was usually made using internal toolingwith a helical impression, acting mainly as a support and shaping mold,and an external tooling acting like one or several rollers. The Europeanpatent application EP 0 510 291 (NUSSBAUM) describes a process formaking an improved thread, in which the thread(s) is(are) shaped bymeans of an internal tooling and an external tooling, both toolingsbeing rotated in a coordinated manner such that sliding takes placebetween the neck material and each tooling. This prevents the neck metalfrom accumulating and folding in front of the external threading tooland being pushed in the direction of advance of the tooling.

[0007] The neck is then cut off on the same device, in other wordswithout having removed the receptacle, leaving a bare surface, in otherwords unprotected and possibly with burrs, on the edge surrounding theorifice.

Problem that Arises

[0008] Even if sliding occurs between the tooling and the neck material,it is impossible to avoid further damage to the varnish. Thus,micro-crazing is observed on the varnish at the thread, both on theouter surface and the inner surface of the neck wall. This crazing makesthe can more sensitive to corrosion by the packaged product.

[0009] Furthermore, with the can thus obtained, it is impossible toposition the distributing head precisely with respect to the edge andthe shoulder. It is difficult to control the position of the heads,which has negative consequences both on the leak tightness of theassembly and on its esthetic appearance.

Purpose of the Invention

[0010] The process according to the invention is a process for themanufacture of a metallic can comprising at least the following steps:

[0011] a) production of a can with a bottom and a cylindrical or shapedwall, for example by deep drawing, drawing and ironing, extrusion orextrusion-drawing, possibly followed by a painting or varnishing depositon at least the inner surface of the cylindrical wall, followed by avarnish annealing treatment;

[0012] b) necking, in order to make a neck on the open end of the can,this step possibly being followed by cutting open end of the neckperpendicular to the center line of the can;

[0013] c) use of a ring with a spindle hole and threaded on its outersurface, and sleeve fitting of the said ring so that its spindle holefits around the neck formed in the previous step, in an operation thatwill subsequently be called “sleeve fitting”:

[0014] and characterized in that it also includes the following step:

[0015] d) plastic expansion of the said neck, the outside diameter ofthe neck being expanded until it is larger than the inside diameter ofthe spindle hole of the ring when unstressed.

[0016] The process is characterized by the use of a ring, for examplemade of a plastic molded ring (but it could be made of any othermaterial—metallic, machined or die forged, etc.), with a globallytoroidal shape, with a cylindrical inner surface that we willsubsequently call the spindle hole, and an outer cylindrical threadedsurface. The diameter of the spindle hole is slightly greater than theoutside diameter of the neck that has just been formed on the can, suchthat the ring can be sleeve fitted into place freely.

[0017] The thread formed on the outer surface of the ring is preferablya standard thread, for example with a

[0018] triangular or trapezoidal section, more suitable for precisepositioning of the distributor head with respect to the metallic can.The thread obtained in prior art, in other words directly by rolling onthe neck, was rounded and consequently imprecise. Furthermore, sincerolling is no longer necessary to form the thread, there is noadditional damage to the varnish on the inner surface of the neck of thecan.

[0019] Finally, the choice of a plastic ring together with adistribution head fitted with an attachment skirt also made of plastic,improves the sealing conditions when the said distribution head is putinto position by screwing.

[0020] A first end of the ring is brought into position facing the canneck that was obtained by necking during the previous step b) and thesaid neck is then inserted inside the spindle hole in the said ring.This is a relative movement; this sleeve fitting operation may also bemade by moving the ring and keeping the can motionless. In this case,this step can be carried out in the same way as the previous and nextsteps, during the same can clamping phase, in other words theseoperations may be carried out on the same machine, the cans being placedon a circular rotating table for which the step by step rotation bringsthem in front of different tools in sequence, each adapted to one ofthese steps, and themselves installed on a circular tool holder plate. Adevice of this type has already been described, for example in FR 1 434177 (LECHNER).

[0021] Since precise positioning of the heads to be fixed on the can isrequired, it is desirable to place the ring precisely on the neck and tocreate a stop system that gives good positioning at the end of sleevefitting. The shape of the first end of the ring can be designed so thatit is recessed and matches the shoulder of the can. It would also bepossible, and preferable, to form a small shoulder on the neck, at acertain distance from the edge of the neck. This distance can be veryprecise when the shoulder is made at the same time as the end of theneck is cut off (optionally) in step b). The ring also has a surfacethat stops in contact with the shoulder formed on the neck. For example,this surface may be obtained by making a shoulder in the spindle hole.The shoulder made on the neck must be sufficiently “high” (radialheight) so that it can act as a stop for the corresponding surface onthe ring while it is being put into position, in other words beforeexpansion of the neck.

[0022] The height of the neck above the spindle hole is controlled bythis stop system acting when the ring is fully sleeve fitted. It isadvantageous to include a subsequent step in which this part projectingbeyond the ring is rolled outwards, so that it traps it and prevents anyaxial backwards movement. Therefore, the projection distance is chosensuch that a rolled edge can be made, for example by stamping. It dependson the outside diameter of the plastic ring and the inside diameter ofthe neck.

[0023] Once the ring has been sleeve fitted and is in contact with theneck, the neck and the ring surrounding it are expanded, for example bystamping, the neck being expanded in the range of plastic deformations(in other words irreversible), the final diameter after elastic recoverybeing slightly greater than the diameter of the spindle hole of the ringat rest, in other words in the initial state free of any mechanicalstress.

[0024] The neck is preferably expanded over its entire length, so as toobtain the largest possible contact surface between the neck and thering after expansion.

[0025] By carrying out this type of deformation and ensuring that theelastic recovery effect of the spindle hole of the ring is greater thanthe elastic recovery effect of the neck, which is easy to ensure whenthe ring is made of a plastic material, a strong bond is obtainedbetween the ring and the neck over the entire contact surface. The bondforce between the ring and the neck depends on the amount of theexpansion and the magnitude of their contact areas. The amount of theexpansion is limited by the ductility of the neck material. The contactsurface, which depends primarily on purely geometric conditions, is aneasier parameter to control.

[0026] Expansion consists of applying a plastic deformation by expandinga metal that has already been strongly deformed during shaping of thecylindrical can (deformation which is particularly high close to thefree edge of the can) and then strong necking. Consequently, the metalis in a very work hardened state, characterized by high mechanicalproperties but low residual ductility.

[0027] The applicant was surprised to observe that this residualductility was actually greater than expected, due to the particulardeformation history imposed on the metal; necking followed bycircumferential expansion, the principal deformation axes remainingparallel to the axial, radial and ortho-radial directions at all times.However, although the metal is more ductile than expected, it isdesirable to allow for a sufficiently large gap between the diameter ofthe ring hole and the initial diameter of the neck formed in step b) tofacilitate sleeve fitting of the ring over the neck, but sufficientlysmall so that expansion will not cause necking, or even rupture of themetal.

[0028] The limiting value that must not be exceeded depends on thenature of the metal and the geometry of the can to be obtained, and canbe determined experimentally using simulation tests reproducing thethermo-mechanical conditions of the various steps in the shaping processconsidered, on the metal considered. Preferably, expansion is carriedout such that it results in an incremental plastic deformation exceeding2% on the inner surface of the neck. The upper limit of this incrementalplastic deformation varies as a function of the ductility of the alloychosen, for which the work hardened state after necking is veryfavorable for good ductility in circumferential expansion.

[0029] In our example applicable to a particular geometry of a can madeof a 1050 A alloy (inside diameter of the neck of the order of 15 mm),the clearance between the hole of the ring and the neck remainsapproximately one tenth of a millimeter, and the inside diameter of theneck after expansion is increased by about 0.3 mm, corresponding to anincremental plastic deformation of about 2% at the inner surface of theneck.

[0030] Therefore at the end of expansion, there is a strong bond overthe entire contact surface between the neck and the hole of the ring.This bond can be quantified by measuring the untightening torquenecessary to separate the ring from the neck, that we will subsequentlycall the sliding torque. In our example, it is found that the slidingtorque exceeds 20 Nm, in other words that it is far greater than torquesnecessary to screw and unscrew the removable head. Standard NF H 35103for glass rings can be used to estimate the order of magnitude of thesetightening torques.

[0031] The process is advantageously followed by the following steps:

[0032] e) rolling, for example by stamping, the end of the neck

[0033] f) smoothing, which consists of moving a roller bearing on theedge of the neck formed by rolling in the previous step, and designed toimprove the surface condition of the varnish layer.

[0034] The edge is rolled preferably outwards, since in this case thering can be fixed in position axially, preventing any axial backwardsmovement. However, the principal function of the rolled edge is toimprove the leak tightness of the assembly, since it forms a roundededge covered with varnish, in other words a toroidal shape with acircular section which is much more suitable to produce a leak tightjoint than the as-cut edge, bare and flat edge, on which burrs may bepresent, used in prior art. Furthermore, this geometry prevents contactbetween the packaged product and the metal edge that is not necessarilyprotected by varnish.

[0035] There is no doubt that the varnished layer is damaged once againduring rolling, resulting in a disturbed surface condition on whichthere are sharp edges and micro-cracks, fairly similar to what isobserved on threads obtained by rolling directly. The next smoothingoperation is designed to improve this surface condition, by closingcrazing and leveling of sharp edges.

[0036] These two additional operations can thus give particularlysatisfactory leak tightness of the can + head assembly.

[0037] If the ring is made of plastic, it is recommended that the stressrelaxation that inevitably takes place in this type of material shouldbe taken into account, and which has the consequence of reducing thetightness a few hours after expansion. Taking account of geometricmanufacturing tolerances, this loosening may be significant, in otherwords sufficient so that the ring can no longer resist the head screwuntightening torque, which would trap it on the can without providingleak tightness. In this situation, the can would then be unsuitable foruse.

[0038] Longitudinal grooves can be made in the hole of the plastic ringin order to prevent the unwanted effects of this loosening. Theapplicant has observed that this type of relief on the surface of thehole, which is easy to produce while the ring is being molded, improvesthe long term tightness between the ring and the neck, no doubt becauseit modifies the distribution and intensity of stresses and therefore theeffect of stress relaxation.

[0039] Additional operations can also be carried out on the neck beforesleeve fitting the ring; for example sanding, scratching, deformation byrolling, machining, allowing at least one pin to project duringmachining of the shoulder that acts as a ring penetration stop. Aninverse thread can also be made on the neck and on the ring, to be surethat it is always possible to unscrew the head even if the ring iscompletely loose.

[0040] Thus, it is possible to make a receptacle according to theinvention with a metal can fitted with the neck, designed to be fixed toany type of removable head (of the eco-refill type), the head beingfitted with fastening means such as a thread, a rim or a click fitgroove, characterized in that it comprises a ring fitted with additionalfastening means other than those on the head, the said ring bonding tothe neck of the metallic can with a sufficiently strong bond to resistthe removable head separation torque.

[0041] The distribution head is usually covered by a protective cap thatis fitted with a cylindrical skirt that extends close to the shoulder ofthe can. For the purposes of this invention, this inner end of the skirtand the lower end of the ring can be fitted with means of preventing thereceptacle from being opened, for example a radial click fit lockingsystem (vertical attachment), or notches inside a breakable lockingstrip (plastic rings with unbreakable notches and multi-notches).

[0042] Due to the presence of the ring used in this invention, it ispossible to have eco-refill type metal cans equipped with reliablelocking systems. The rolling means used in prior art resulted in arounded and imprecise thread, but could not be used to make asufficiently sharp relief capable of trapping a locking strip. However,with the ring according to this invention, this sharp relief is easy toform during molding, for example by increasing the outside diameter atthe first end of the ring.

[0043] This end thus acts as a mating ring, the edge of which can trap alocking strip, for example connected to the inner end of a cap skirt byseveral breakable bridges, like the ring described in EP 0 107 680. Thisring can also be fitted with ratchet teeth, and the locking meansdescribed in FR 2 665 142 can be reproduced. This latter system has theadvantage that a large torque is not necessary to separate the strip.

[0044] The process according to the invention will be better understoodafter reading the detailed description of a particular embodiment,presented as a non-limitative example.

EXAMPLE EMBODIMENT OF THE INVENTION

[0045]FIG. 1 shows a can with a threaded neck according to prior artassociated with the bottom part of a distribution head provided with ahole in which a pump can be fitted in order to distribute the product inthe spray form.

[0046]FIG. 2 shows a can with a threaded neck designed for theattachment of an aerosol distributor made according to the invention.

[0047]FIG. 3 shows a diametric half-section of an enlarged view of theneck and the ring obtained by the process according to the invention,after the ring has been sleeve fitted, the neck has been expanded andthe free edge of the neck has been rolled. This same figure shows thefree end of the neck before rolling, in dashed lines.

[0048] The can 1 illustrated in FIG. 2 is made of a 1050A aluminumalloy. It is composed of a bottom 2 and a cylindrical wall 3 withdiameter 35 mm. Its free end has been formed into an approximatelycylindrical neck 4 with height and diameter equal to approximately 10 mmand 15 mm respectively. The ring 5 is made of polypropylene. It is heldfixed onto neck 4 by expansion of the neck made according to theinvention and by rolling the end 48 of the neck 4 leading to theformation of a rounded edge 6, in other words with a circular toroidalshape, and always coated with varnish. The edge 6 forms the edge(rounded in this case) of the open end of the can surrounding itsorifice 7.

[0049] The ring 5, more easily seen on the half-section in FIG. 3, is ofmolded polypropylene. Its shape is globally toroidal, with a spindlehole 52 and an external cylindrical surface 55 on which a thread 54 isformed. The diameter of the spindle hole 52 is slightly greater than theoutside diameter of the neck of the can obtained by necking (average 0.1mm, maximum 0.3 mm), such that the ring may be sleeve fitted withoutapplying force. The thread 54 formed on the outer surface 55 of the ring5 is a standard thread with a triangular section. The ring also has ashoulder 53 formed in the spindle hole 52, the small ledge beingdesigned to form a stop on the shoulder 41 formed on the neck 4 of thecan after the ring 5 has been fully sleeve fitted on neck 4.

[0050] The process for making the can in this example comprises theconventional steps for making an aluminum allow aerosol can:

[0051] slugs made of 1050 A aluminum alloy

[0052] tumbling of slugs in the presence of a lubricant such as zincstearate

[0053] impact extrusion of the slugs, possibly followed by one orseveral drawing passes

[0054] trimming of the end

[0055] stripping, designed to eliminate traces of extrusion and drawinglubricants

[0056] deposition of varnish by spraying on the inner surface, followedby baking at about 200-265° C. designed to dry and polymerize the saidvarnish

[0057] deposition of a coat of lacquer with a roller, followed by drying

[0058] the can decor is printed, usually by offset, and possiblyfollowed by an overprinting varnish and baking again

[0059] the cans are put into position on a circular table rotating stepby step, bringing each can in front of a different tool in each step,the tools being adapted to the different phases described below, thesetools themselves being mounted on a circular tool holder plate.

[0060] formation of the neck and cutting of the free edge. Necking isdone gradually by stamping in several passes with shaping dies, thefinal die matching the required shape of the shoulder. While cutting thefree edge 49 of the neck 4, a small shoulder 41 is formed on the neck ata precise distance from the top end 49 of the neck 4.

[0061] sleeve fitting the ring A first end 51 of the ring 5 is put intoposition facing neck 4 of can 1 which was obtained by necking during theprevious step, and ring 5 is then sleeve fitted on neck 4. When theshoulder 53 formed in the spindle hole 52 of the ring 5 stops in contactwith the shoulder 41 on neck 4, the ring 5 is retained in this position.This stop system acting after the ring has been sleeve fitted, controlsthe height of the part 48 of neck 4 that projects from the spindle hole52. In this case it is of the order of 2 mm. The first end 51 of thering is molded such that it acts as a mating ring 56 on which a lockingstrip can be fixed.

[0062] Expansion Once the ring has been sleeve fitted and held incontact with the ring, the neck 4 and the ring 5 are expanded bystamping until the diameter of the outer surface 42 of the neck 4 isgreater than the diameter of the spindle hole 52 of the ring 5 at rest,after elastic recovery. In this case expansion is done by stamping, inother words using an internal tool that is inserted in the orifice andthen applying pressure to the free edge. The conical and thencylindrical shape of the stamping tool imposes a plastic expansion thatincreases the diameter of the outer surface 42 of the neck 4 by about0.5 mm, over the entire length L of the cylindrical part of the neck.This thus gives a strong bond over the entire contact surface betweenthe neck and the hole of the ring. The spindle hole of the ring ismarked with longitudinal striations, which eliminates any risk ofloosening due to stress relaxation that occurs sometimes afterexpansion.

[0063] rolling and smoothing The end 48 of the neck 4 projecting fromthe ring is then rolled by stamping. The rounded edge 6 thus formedfixes the ring in position axially, and in particular forms a roundededge, always covered with varnish, improving the tightness of screwedcan + head assemblies. The next smoothing operation, designed to improvethe surface condition of the varnish at the rounded rolled edge,consists of passing the roller over the said rolled edge with a very lowpressure, just sufficient to smooth off rough edges created on thevarnish and to close off cavities created during the previous steps.

[0064] With this geometry (inside diameter of the neck of the order of15 mm), the ring according to the invention is rigidly fixed on thebottle neck since it resists a sliding torque exceeding 20 Nm. Thisvalue can then be compared with the range of values of unscrewingtorques to be applied to cap rings (between 2 and 8 Nm), particularly instandard AFNOR NF H 35103 (glass rings and caps).

Advantages of the Process According to the Invention

[0065] This process can be used to make eco-refill type cans.

[0066] The interchangeable head can easily be detached from the can, sothat each part used in the assembly can easily be recovered andrecycled.

[0067] The varnish is less damaged on the inner surface of the neck,which makes the can less sensitive to corrosion by the product containedin it.

[0068] The ring is positioned such that the distributor head is fixed inleaktight manner and is in a precise and repeatable position with acontrolled clearance between the skirt and the shoulder, favorable toimproving the esthetic appearance of the assembly.

[0069] For the first time, an eco-refill type metallic can can be fittedwith a distribution head protected by a locking strip.

1. Process for manufacturing a metal can (1) equipped with a threadedneck on which any type of removable head can be fitted, comprising atleast the following steps: a) production of a can with a bottom and acylindrical or shaped wall b) formation of a neck (4) at the open end ofthe can c) use of a ring (5) equipped with a spindle hole (52) and athread (54) over its outer surface (55), and sleeve fitting of said ring(5) by driving its spindle hole (52) around the neck (4) formed in theprevious step, and characterized in that it also includes the followingstep: d) plastic expansion of the said neck (4), the diameter of theouter surface (42) of the neck (4) being expanded to exceed the value ofthe inner diameter of the spindle hole (52) of the ring (5) when atrest.
 2. Manufacturing process for a metal can (1) equipped with athreaded neck according to claim 1 , characterized in that the saidplastic expansion of the neck (4) corresponds to an incremental plasticdeformation equal to at least 2% at the inner surface of the neck. 3.Manufacturing process for a metal can (1) equipped with a threaded neckaccording to claim 1 , characterized in that the shoulder (41) formed onthe neck (4), designed to act as a stop when ring (5) is fully sleevefitted on the neck (4) formed in step c).
 4. Manufacturing process for ametal can (1) equipped with a threaded neck according to claim 1 ,characterized in that a plastic ring (5) is used.
 5. Manufacturingprocess for a metal can (1) equipped with a threaded neck according toclaim 1 , characterized in that a ring (5) is used with a height suchthat after the said ring has been sleeve fitted onto the neck (4), apart (48) of the said neck (4) projects beyond the ring (5), and thatthe previous steps in the process are followed by rolling the saidportion (48) projecting beyond the ring (5) in order to make a rollededge (6).
 6. Manufacturing process for a metal can (1) equipped with athreaded neck according to claim 5 , characterized in that it isfollowed by a final step to smooth the rolled edge (6).
 7. Receptaclewith a metal can (1) equipped with a neck (4) and designed to be fixedto any type of removable head, the said removable head being providedwith fastening means, characterized in that it comprises a ring (5)equipped with fastening means (54) complementary to the means on thehead, the said ring bonding to the neck (4) of the metal can (1) with asufficiently strong force to resist the removable head separationtorque.
 8. Receptacle with a metal can (1) equipped with a neck (4)fastened by screwing with a removable head, characterized in that thesaid receptacle is provided with locking means.